1. Field of the Invention
The present invention pertains to a system for remotely monitoring temperature, and more particularly to a system for monitoring the temperature in heated or refrigerated trailers during transit to prevent the spoilage of a perishable cargo caused by temperature fluctuations.
2. Description of the Prior Art
An important requirement in transporting goods requiring a controlled environment is communicating the variances and failures of the environmental control device to outside persons to make the necessary corrections or repairs. More specifically, when transporting perishable foodstuffs and the like the temperature in the transport container must be controlled to prevent spoilage of the cargo. While current refrigeration technology is quite reliable, equipment failures and changes in the ambient temperature do cause the temperature in the container to change, becoming either too warm or too cold thereby causing spoilage of the cargo and substantial monetary loss. Frequently, the driver is unaware of the temperature changes and continues to operate for some time while the cargo is spoiling and losses are increasing.
Previously, monitors of the temperature of a refrigerated container have ranged from simple gauges having a sensor disposed within the container and an external readout means which often required the driver to stop and climb up on the truck to read the gauge which provided no method whereby the driver could determine the temperature while in motion. U.S. Pat. No. 4,455,096 issued June 19, 1984 to Brandstedt is an improvement by providing an externally readable display so as the driver can see the temperature readout while the vehicle is in motion. Brandstedt, though, has the dual disadvantages of requiring holes to be made in the container to access its sensor and requiring the driver to periodically read the display, as no out of range alarm is provided.
U.S. Pat. No. 4,024,495 issued May 17, 1977 to O'Brien discloses an improvement over Brandstedt by placing the temperature sensor in the refrigerated unit and the detector in the cab with the driver. O'Brien, however, requires a linear electrical transducer, a device difficult to obtain and usually quite expensive; and further is an analog device with a drifting calibration due to the changes in power source and aging of the components.